1. Field of the Invention
The present invention relates to a system for determining the pressure of a pneumatic tire for use on a motor vehicle such as an automobile, and more particularly to an improvement in such a pneumatic tire pressure determining system for determining the pressure of a pneumatic tire highly accurately.
2. Description of the Prior Art
Known pneumatic tire pressure determining systems are disclosed in Japanese patent publication No. 56-10202 and Japanese laid-open patent publication No. 63-305011, for example.
The pneumatic tire pressure determining system disclosed in Japanese laid-open patent publication No. 56-10202 has pressure sensors attached to respective road wheels. The pneumatic tire pressure determining system disclosed in Japanese laid-open patent publication No. 63-305011 detects the angular velocities of road wheels, and compares the angular velocity of each of the road wheels with the average value of the angular velocities of the road wheels for determining a reduction in the pneumatic pressure in any of the tires of the road wheels.
The pneumatic tire pressure determining system disclosed in the latter publication cannot determine the pneumatic tire pressures highly accurately and hence is not highly reliable. Specifically, because only the angular velocities of the road wheels are used as a reference value, the difference between radii of curvature of paths of the road wheels cannot be calculated while the motor vehicle is making a turn. The steering system of the motor vehicle tends to suffer a mechanical error even when the motor vehicle is running straight. Consequently, the disclosed pneumatic tire pressure determining system can determine a reduction in the pneumatic tire pressure only in a certain range of motor vehicle motions.